April 3 (Reuters) - A strong 7.8 magnitude earthquake struck off northern Chile late on Wednesday, the U.S. Geological Survey said.

The quake, the largest of a series of aftershocks following a powerful and deadly 8.2 magnitude quake that hit a day earlier, was located 12 miles (19 km) south of the port of Iquique at a relatively shallow depth of 12.4 miles (20 km), the USGS said.

It was earlier reported as a 7.4 magnitude quake.

The Pacific Tsunami Warning Center said there was no widespread tsunami threat, but that the latest tremor could generate a local tsunami.

Chile's emergency office said it ordered a preventative evacuation of the coastal area.